Process and apparatus for vaporizing corrosive liquids



l) 0- H. KIEWEG 2,202,800

PROCESS AND APPARATUS FOR VAPORIZING CORROSIVE LIQUIDS Filed Feb. 3, 1938 2 SheetsSheet 1 F i g. 1

Invenfor:

K n W W Arforney.

May 28, 1940. H. KIEWEG 2,202,800

PROCESS AND APPARATUS FOR VAPORIZING CORROSIVE LIQUIDS Fi led Feb. s, 1938 2 Sheets-Sheet 2 Fig.2

Patented May 28, 1940 Ui'i'il STATES PATENT OFFiCE PROCESS AND APPARATUS FOR VAPORIZ- ING- CORRDSIWE LIQUIDS Application February 3, 1938, Serial No. 188,513

8 Claims.

My invention relates to the vaporization of corrosive liquids, and more particularly to an improved procedure and apparatus therefor.

In the vaporization of corrosive liquids it has been necessary to employ materials highly re sistant to corrosion for the construction of the vaporizing apparatus. This has necessitated the use of construction materials which in most cases are relatively very expensive, and which have other undesirable characteristics such as low pressure resistance and low resistance to mechanical and thermal shock. In the vaporization of nitric acid, for example, even acid resistant chromium steels are rapidly corroded by the hot liquid nitric acid, necessitating the use of precious metals, or of high silicon iron or refractory materials, both of the latter having low resistance to pressure, mechanical shock, and thermal shock. In addition to iron, nitric acid in the liquid form attacks other metals such as, for example, (Divers, Trans. Chem. Soc. 1883, 43, 443; 1885, 47, 231) copper, silver, mercury, bismuth, zinc, magnesium, aluminium, cadmium, tin, lead, and the alkali metals, while the vapors of nitric acid have been reported (E. Montignie, Bull. soc. chim. (5), 2, 2260-1) not to attack the following: calcium, magnesium, aluminium, cadmium, iron, bismuth, copper, zinc, lead, tin, and manganese.

I have now discovered a process and apparatus whereby such vaporizations may be effected by the use of vessels having walls which are corrodible by the hot liquid being vaporized. By the use of my invention it is thus possible to employ vessels constructed of materials which are relatively inexpensive, and which have the necessary resistance to pressure and shock. A resulting advantage of my invention is that vaporizations may be carried out under relatively high pressures. Such a procedure is desirable, for example, in vaporizing nitric acid for use in high pressure vapor phase nitration reactions.

My improved process comprises, briefly, vaporizing the corrosive liquid by contact with hot gas while maintaining the liquid out of contact with the walls of the vessel in which the liquid-gas contact is effected. By this means only the relatively much less corrosive vapors come in contact with the vessel walls and the highly corrosive action of the hot liquid is entirely avoided. To

effect this end I introduce the liquid into the vaporizing vessel at a substantial distance from the vessel walls and cause hot gas to flow through the vessel at such a rate that the liquid is vaporized before it is carried to the vessel walls by the action of gravity, convection currents, or otherwise. It is evident that my process may be carried out with various types of apparatus, as for example, in towers in which the corrosive liquid is dropped through a rising current of hot gas, or in large vessels in which the liquid is sprayed centrally into a current of hot gas.

My invention will be specifically described with relation to a preferred form of apparatus which is illustrated in the accompanying drawings. One modification of this apparatus is shown in sectional elevation in Figure I of the drawings, and a second modification is shown in sectional elevation in Figure II.

Referring to Figure I, the apparatus may be 1 seen to comprise essentially a vessel I, filled'with packing material 2, and supplied with means for introducing hot gas and the liquid to be vaporized, and means for removing the resulting vapor-laden gas. The vessel i may be constructed of material which is not resistant to corrosion by the hot liquid to be vaporized, but should preferably be highly resistant to corrosion by the resulting vapors. This vessel may be of conventional form such as a cylindrical vessel fitted with a flanged closure, as illustrated in the drawings. The packing material 2, contained in the vessel I may constitute crushed refractory material, glass beads, or other packing which is resistant to the action of the hot liquid being vaporized. Means for introducing the liquid to be vaporized may be provided in the form of a pipe 3, leading to the top central portion of the packing material 2; and means for introducing the hot gas may suitably constitute an entrance port 4 in the central portion of the bottom of the vessel l. Means for removing the vapor-laden gas may comprise a pipe 5, communicating with the interior of the vessel l at the top thereof, and preferably at a point substantially spaced from the orifice of the pipe 3.

Although the apparatus as above described includes the essential features for satisfactory operation, I prefer to utilize further improvements, comprising means for maintaining the vessel walls at a temperature above the boiling point of the liquid being vaporized, and means for directing the gas flow through the packing material to secure more efficient liquid-gas contact.

Any suitable heating means may be provided for maintaining the vessel walls at a temperature above the boiling point of the liquid being vaporized, such as a conventional heating bath as illustrated in the drawing. For this purpose an outer vessel 6 is provided, containing a liquid heat fiow from the pipe 3.

transfer medium 1. This heating bath preferably also serves to heat the gas utilized for vaporizing the corrosive liquid. To efiect this end, there is placed in the bath a heating coil 8, terminating in the port 4 which communicates with the interior of the vessel 1.

In order to secure eflicient liquid-gas contact, I provide means for causing the hot gas to flow through the packing material 2 in the path of normal gravitational fiow of the liquid through this packing material. Such means may suitably comprise annular bafiies 9-9 horizontally disposed in the packing material 2, and having their outer edges closely adjacent or contacting the side walls of the vessel I. The inner edges of the baflles 9-9 should define a volume of the packing material 2 slightly larger than the volume occupied by liquid in normal gravitational For this purpose the inner edges of the baflles 9-43 may suitably define a cone of approximately 60 having its apex at a point somewhat above the orifice of the pipe 3.

The modification of the apparatus illustrated in Figure II of the drawings is identical with that of Figure I with the exception that the baffles 99 are omitted and the side walls of the vessel I are utilized to direct the gas flow efficiently through the packing material 2. In this case the vessel walls define a cone having a volume slightly greater than the volume occupied by liquid in normal gravitational flow from the pipe 3 through the packing 2. As in the case of the baffles referred to above, the vessel walls in this case may suitably define a cone of approximately 60 having its apex at a point on the pipe 3 substantially above its orifice.

The operation of my process will be specifically described with reference to the vaporization of nitric acid in the above described apparatus. For this purpose the vessel I may be constructed of chromium steel, and the packing 2 may constitute glass beads, crushed vitrified alumina, porcelain Raschig rings, small pieces of Duriron (high silicon iron), or the like. The apparatus may be of pressure resistant construction, and the vaporization may be effected at any desired pressure.

For vaporizing nitric acid the heat transfer medium 1 may suitably be maintained at a temperature of the order of 250-350 C. and any of the known eutectic salt mixtures utilized for such temperature ranges may be employed for this purpose. A gas which is inert in the presence of hot nitric acid, such as nitrogen or carbon dioxide, or a gas or vapor which is subsequently to be reacted with the nitric acid vapors may be utilized for the vaporization. The gas is passed through the heating coil 8 into the bottom of the vessel 1 by means of the entrance port 4. The nitric acid is introduced through the pipe 3 and flows downward through the packing material 2 counter-currently to the rising current of gas. The gas and nitric acid vapors leave the apparatus through the pipe 5.

The rate at which the nitric acid is introduced should not exceed the rate at which normal gravitational flow will take place in the packing material. That is, the packing should not be allowed to become flooded with the result that liquid nitric acid comes in contact with the side walls of the vessel. The rate of gas fioW should not be sufficiently high to mechanically carry droplets of liquid nitric acid to the top of the vessel or through the exit pipe. However, the rate of flow of the gas and the heat content thereof should be suificient to insure complete vaporization of the nitric acid before normal gravitational flow carries liquid to the bottom of the vessel or to the lower portions of the side walls. The rate of flow and heat content of the gas may be adjusted to provide an adequate factor of safety in this respect, and an even further safeguard is provided by maintaining the vessel walls above the boiling point of the liquid, by means of external heating.

It will, of course, be evident that my process is applicable to the vaporization of corrosive liquids generally, as Well as to the vaporization of nitric acid. Similarly, my process may be carried out with various other forms of apparatus, and numerous modifications may be made in the structure of the preferred type of apparatus described herein. In general it may be said that any such modifications, and the use of any equivalents which would naturally occur to those skilled in the art, are included in the scope of my invention.

My invention now having been described, what I claim is:

1. In an apparatus for vaporizing a corrosive liquid by contact with hot gas, the combination of a vessel having walls corrodible by said liquid, and containing a packing of material resistant to corrosion by said liquid, means for introducing said liquid into the top portion of said packing, centrally thereof, means for passing the said hot gas through said packing, and means for defining a cone to confine the path of gas flow substantially to the path of gravitational fiow of said liquid through said packing.

2. In an apparatus for vaporizing a corrosive liquid by contact with hot gas, the combination of a vessel having walls corrodible by said liquid, and containing a packing of material resistant to corrosion by said liquid, means for introducing said liquid into the top portion of said packing, centrally thereof, and annular baffles horizontally disposed in said packing to confine the path of gas flow substantially to the path of gravitational flow of said liquid through said packing.

3. In an apparatus for vaporizing a corrosive liquid by contact with hot gas, the combination of a vessel having walls corrodible by said liquid, and containing a packing of material resistant to corrosion by said liquid, and means for introducing said liquid into the top portion of said packing, centrally thereof, the walls of said vessel defining a cone to confine the path of gas flow substantially to the path of gravitational flow of said liquid through said. packing.

4. In an apparatus for vaporizing a corrosive liquid by contact with hot gas, the combination of a vessel having walls corrodible by said liquid, and containing a packing of material resistant to corrosion by said liquid, means for introducing said liquid into said packing at a substantial distance from the said vessel walls, means for defining a cone to confine the path of gas flow substantially to the path of gravitational flow of said liquid through said packing means for simultaneously heating the said gas and externally heating the said vessel walls, and means for passing the hot gas through said packing.

5. A process for vaporizing a corrosive liquid by contact with hot gas in a vessel containing packing material extending to the Walls of said vessel, said packing material being resistant to corrosion by said liquid, while maintaining the liquid out of contact with the walls of said vessel, which comprises heating the walls of said vessel to a temperature above the boiling point of said corrosive liquid, introducing the said liquid into the top portion of said packing material, centrally thereof, and at a point substantially spaced from the walls of the said vessel, and passing hot gas through said packing material, the point of introduction of said liquid being so spaced from the said vessel walls, and the temperatures of said liquid and said gas and the rates of introduction of said liquid and said gas being so correlated, as to vaporize said liquid while in contact with said packing material, and without any substantial contact of liquid with said vessel walls. 6. A process for vaporizing a corrosive liquid by contact with hot gas in a vessel containing packing extending to the walls of said vessel, said packing material being resistant to corrosion by said liquid, while maintaining the liquid out of contact with the walls of said vessel, which comprises heating the walls of said vessel to a temperature above the boiling point of said corrosive liquid, introducing the said liquid into the top portion of said packing material, centrally thereof, and at a point substantially spaced from the walls or" the said vessel, passing hot gas through said packing material, and confining the flow of said gas through said packing material substantially to the path of gravitational flow of the said liquid through said packing material, the point of introduction of said liquid being so spaced from said vessel walls, the temperatures of said liquid and said gas and the rates of said introduction of said liquid and said gas being so correlated, as to vaporize said liquid while in contact with said packing material, and without any sub stantial contact of liquid with said vessel walls.

7. A process for vaporizing nitric acid by contact with hot gas in a vessel containing packing material extending to the walls of said vessel, said packing material being resistant to corrosion by said nitric acid, while maintaining the nitric acid out of contact with the walls of said vessel, which comprises heating the Walls of said vessel above the boiling point of said nitric acid, introducing the said nitric acid into the top portion of said packing material centrally thereof, and at a point substantially spaced from the walls of the said vessel, passing hot gas through said packing material, the point of introduction of said nitric acid being so spaced from the said vessel walls, and the temperatures of said nitric acid and said gas and the rates of introduction of said nitric acid and said gas being so correlated, as to vaporize said nitric acid while in contact with said packing material, and without any substantial contact of liquid with said vessel walls.

8. A process for vaporizing nitric acid by contact with hot gas in a vessel containing a packing material extending to the walls of said vessel, said packing material being resistant to corrosion by said nitric acid, while maintaining the nitric acid out of contact with the walls of said vessel, which comprises heating the walls of said vessel above the boiling point of said nitric acid, introducing the said nitric acid into the top portion of said packing material, centrally thereof, and at a point substantially spaced from the walls of the said vessel, passing hot gas through said packing material, and. confining the flow of said gas through said packing. material substantially to the path of gravitational flow of the said liquid through said packing material, the point of introduction of said nitric acid being so spaced from said vessel walls, the temperatures of said liquid and said gas and the rates of introduction of 9 said liquid and said gas being so correlated, as to vaporize said nitric acid while in contact with said packing material, and without any substantial contact of liquid with said vessel walls.

HOME-R. KIEWE'G. 

